Fault detection for parallel inverters system

ABSTRACT

According to one aspect, embodiments of the invention provide a method of operating a UPS system having a first UPS and a second UPS, the method comprising coupling at least one control line between the first UPS and the second UPS to operate the first UPS and the second UPS in a parallel mode of operation, providing output power from each of the first UPS and the second UPS to a load, detecting a fault condition in the UPS system, decoupling the at least one control line, operating the first UPS in a diagnostic mode of operation, and determining if the fault condition is associated with the first UPS.

BACKGROUND OF INVENTION

1. Field of the Invention

At least one example in accordance with the present invention relatesgenerally to the parallel control of Uninterruptible Power Supplies.

2. Discussion of Related Art

Uninterruptible Power Supplies (UPS) are commonly used to provideregulated, uninterrupted power for sensitive and/or critical loads.There is an increased desire for UPS systems to provide greater capacityand/or reliability. For example, to provide enhanced scalability and/orredundancy, two UPS's may be electrically connected to form a singleparallel UPS system with one output. In such a system, the combinationof two UPS's may provide increased power capacity to a load attached tothe parallel UPS system. Also, if a first one of the UPS's coupled inparallel fails, the second one of the UPS's coupled in parallel maybackup for the failed UPS.

SUMMARY OF THE INVENTION

Aspects in accord with the present invention are directed to a method ofoperating a UPS system having a first UPS and a second UPS. In oneaspect, the present invention features a method comprising coupling atleast one control line between the first UPS and the second UPS tooperate the first UPS and the second UPS in a parallel mode ofoperation, providing output power from each of the first UPS and thesecond UPS to a load, detecting a fault condition in the UPS system,decoupling the at least one control line, operating the first UPS in adiagnostic mode of operation, and determining if the fault condition isassociated with the first UPS.

According to one embodiment, the method further comprises operating thesecond UPS in a diagnostic mode of operation, and determining if thefault condition is associated with the second UPS. In anotherembodiment, determining if the fault condition is associated with thesecond UPS includes coupling a diagnostic module to the second UPS.

According to another embodiment, coupling at least one control linebetween the first UPS and the second UPS includes coupling a connectionmodule between the first UPS and the second UPS, and wherein decouplingthe at least one control line further includes decoupling the connectionmodule from the first UPS and coupling a diagnostic module to the firstUPS. In one embodiment, coupling at least one control line between thefirst UPS and the second UPS includes coupling a connection modulebetween the first UPS and the second UPS, and wherein decoupling the atleast one control line, includes changing a state of the connectionmodule from an operational state to a diagnostic state.

According to one embodiment, operating the first UPS in the diagnosticmode of operation includes disabling a bypass mode of operation of thefirst UPS. In one embodiment, operating the first UPS in the diagnosticmode of operation includes conducting a self-test of an inverter of thefirst UPS.

In another aspect, the present invention features a UPS systemcomprising a first UPS and a second UPS, each of the first UPS and thesecond UPS including a first input to receive input power from a firstpower source, a battery configured to provide battery power, an outputcoupled to provide output power, output power circuitry coupled to theoutput and configured to provide the output power derived from at leastone of the first power source and the battery, a first I/O, a secondI/O, and control circuitry coupled to the first I/O and the second I/O,and a connection module coupled to the first I/O, the second I/O and theoutput of the first UPS and coupled to the first I/O, the second I/O andthe output of the second UPS, the connection module having an outputthat provides output power from at least one of the first UPS and thesecond UPS, wherein the first UPS is configured to operate in adiagnostic mode based on a signal detected at the second I/O of thefirst UPS, and configured in the diagnostic mode to determine if a faultof the UPS system is associated with the first UPS.

According to one embodiment, the connection module is configured tooperate in a diagnostic mode to couple the first I/O of the first UPS tothe second I/O of the first UPS. In another embodiment, the systemfurther comprises a diagnostic module configured to be coupled to thefirst UPS in the diagnostic mode and configured to couple the first I/Oof the first UPS to the second I/O of the first UPS.

According to another embodiment, the first UPS includes an inverter, andwherein the first UPS is configured to conduct an inverter test in thediagnostic mode. In one embodiment, the first UPS is further configuredto operate in a bypass mode of operation, and wherein the controlcircuitry is configured to disable the bypass mode of operation in thediagnostic mode. In another embodiment, the second UPS is configured tooperate in a diagnostic mode based on a signal detected at the secondI/O of the second UPS, and configured in the diagnostic mode, todetermine if a fault of the UPS system is associated with the secondUPS.

According to one embodiment, the connection module is configured tooperate in a diagnostic mode to couple the first I/O of the second UPSto the second I/O of the second UPS. In another embodiment, the systemfurther comprises a diagnostic module configured to be coupled to thesecond UPS in the diagnostic mode and configured to couple the first I/Oof the second UPS to the second I/O of the second UPS.

In one aspect, the present invention features a UPS system comprising afirst UPS and a second UPS, each of the first UPS and the second UPSincluding a first input to receive input power from a first powersource, a battery configured to provide battery power, an output coupledto provide output power, output power circuitry coupled to the outputand configured to provide the output power derived from at least one ofthe first power source and the battery, a first I/O, a second I/O, andcontrol circuitry coupled to the first I/O and the second I/O, and aconnection module coupled to the first I/O, the second I/O and theoutput of the first UPS and coupled to the first I/O, the second I/O andthe output of the second UPS, the connection module having an outputthat provides output power from at least one of the first UPS and thesecond UPS, and means for detecting a fault in the UPS system and forisolating the fault to one of the first UPS and the second UPS.

According to one embodiment, the means for detecting a fault includemeans for disabling the output of the first UPS and the output of thesecond UPS after detection of a fault. In one embodiment, each of thefirst UPS and the second UPS includes parallel control circuitry foroperating the first UPS and the second UPS in a parallel mode ofoperation, and wherein the means for detecting a fault includes meansfor detecting a fault in the parallel control circuitry of one of thefirst UPS and the second UPS.

According to another embodiment, the system further comprises means forestablishing one of the first UPS and the second UPS as a master UPS ofthe UPS system. In one embodiment, the master UPS is configured tocontrol an output of an inverter in the first UPS and an output of aninverter in the second UPS.

In one aspect, the present invention features a method of operating aUPS system having a first UPS, the method comprising powering on thefirst UPS, detecting a first signal at a first I/O of the first UPSusing a first detection circuit of the first UPS, detecting a secondsignal at a second I/O of the first UPS using a second detection circuitof the first UPS, based on a status of the first signal and a status ofthe second signal, configuring the first UPS to operate in one of amaster mode of operation and a controlled mode of operation.

According to one embodiment, the method further comprises operating thefirst UPS in the master mode of operation, in the master mode ofoperation generating in the first UPS an output control signal andproviding the output control signal at a third I/O of the first UPS, andcontrolling operation of an output inverter of the first UPS using theoutput control signal. According to another embodiment, the methodfurther comprises operating the first UPS in the controlled mode ofoperation, in the controlled mode of operation, receiving an inputcontrol signal at a fourth I/O of the first UPS, and controllingoperation of the output inverter of the first UPS using the inputcontrol signal.

According to one embodiment, the UPS system further includes a secondUPS coupled in a parallel configuration with the first UPS, and whereinthe method further includes powering on the second UPS, detecting athird signal at a first I/O of the second UPS using a first detectioncircuit of the second UPS, detecting a fourth signal at a second I/O ofthe second UPS using a second detection circuit of the second UPS, basedon a status of the third signal and a status of the fourth signal,configuring the second UPS to operate in one of a master mode ofoperation and a controlled mode of operation.

According to another embodiment, the method further comprisesconfiguring the first, second, third and fourth signals, such that atany given time only one of the first UPS and the second UPS isconfigured in the master mode of operation and only one of the first UPSand the second UPS is configured in the controlled mode of operation.According to one embodiment, the method further comprises coupling thesecond I/O of the first UPS to the first I/O of the second UPS, andcontrolling operation of an output inverter of the second UPS using acontrol signal generated by the first UPS. In one embodiment, the methodfurther comprises detecting a fifth signal at a fifth I/O of the firstUPS, and configuring the first UPS to operate in a stand-alone mode ofoperation.

In another aspect, the present invention features a UPS comprising afirst input to receive input power from a first power source, a secondinput to receive input power from a second power source, an outputcoupled to provide output power, output power circuitry coupled to theoutput and configured to provide the output power derived from at leastone of the first power source and the second power source, a first I/O,a second I/O, and control circuitry coupled to the first I/O and thesecond I/O and configured to control the UPS to operate in one of amaster mode of operation and a controlled mode of operation based onfirst and second control signals at the first I/O and the second I/O,wherein the control circuitry in the master mode of operation isconfigured to generate a control signal to control the output powercircuitry, and in the controlled mode of operation is configured toreceive a control signal from an external device to control the outputpower circuitry.

According to one embodiment, the UPS further comprises a third I/Ocoupled to the control circuitry and configured to receive a thirdcontrol signal, and wherein the control circuitry is further configuredto operate the UPS in one of a stand-alone mode and a parallel modebased on a status of the third control signal. In another embodiment,the UPS further comprises a bypass switch coupled to the first input,the output and the control circuitry and operable under control of thecontrol circuitry to selectively couple the first input to the output toprovide in a bypass mode of operation the input power from the firstpower source at the output bypassing the output power circuitry.

According to another embodiment, the UPS further comprises a fourth I/Ocoupled to the control circuitry and configured to receive a fourthcontrol signal, and wherein the control circuitry is further configuredto inhibit bypass mode of operation based on a status of the fourthcontrol signal. In another embodiment, the UPS further comprises a fifthI/O coupled to the control circuitry and configured to receive a statussignal from a parallel connected UPS, and wherein the control circuitryis configured to change an operational mode of the UPS from controlledmode of operation to master mode of operation based on a state of thestatus signal.

In one aspect, the present invention features a UPS system comprising afirst UPS and a second UPS, each of the first UPS and the second UPSincluding a first input to receive input power from a first powersource, a battery configured to provide battery power, an output coupledto provide output power, output power circuitry coupled to the outputand configured to provide the output power derived from at least one ofthe first power source and the battery, a first I/O, a second I/O, andcontrol circuitry coupled to the first I/O and the second I/O andconfigured to set a mode of operation as one of a master mode ofoperation and a controlled mode of operation based on first and secondcontrol signals at the first I/O and the second I/O, wherein the controlcircuitry in the master mode of operation is configured to generate acontrol signal to control the output power circuitry, and in thecontrolled mode of operation is configured to receive a control signalfrom an external device to control the output power circuitry, and aconnection module coupled to the first I/O, the second I/O and theoutput of the first UPS and coupled to the first I/O, the second I/O andthe output of the second UPS, the connection module having an outputthat provides output power from at least one of the first UPS and thesecond UPS.

According to one embodiment, the connection module is configured tocouple the second I/O of the first UPS to the first I/O of the secondUPS to configure the first UPS for operation in the master mode ofoperation and to configure the second UPS in the controlled mode ofoperation. In another embodiment, the connection module is coupled tothe control input and the control output of each of the first UPS andthe second UPS and configured to couple the control input of the firstUPS to the control output of the second UPS and to couple the controloutput of the first UPS to the control input of the second UPS.

According to another embodiment, each of the first UPS and the secondUPS further includes a control input configured to receive the controlsignal from the connection module in the controlled mode of operationand a control output to provide the control signal in the master mode ofoperation. In one embodiment, each of the first UPS and the second UPSincludes a bypass switch coupled to the input, the output and thecontrol circuitry and operable under control of the control circuitry toselectively couple the input to the output to provide in a bypass modeof operation the input power from the first power source at the outputbypassing the output power circuitry.

According to one embodiment, each of the first UPS and the second UPSincludes a bypass input coupled to the control circuitry and configuredto receive a bypass control signal, and wherein the control circuitry isfurther configured to inhibit bypass mode of operation based on a statusof the fourth control signal. In another embodiment, each of the firstUPS and the second UPS includes a bypass output, and wherein theconnection module is configured to couple the bypass input of the firstUPS to the bypass output of the second UPS and to couple the bypassoutput of the first UPS to the bypass input of the second UPS. In oneembodiment, each of the first UPS and the second UPS includes a statusinput coupled to the control circuitry and configured to receive astatus signal from the connection module, and wherein the controlcircuitry is configured to change an operational mode of the UPS fromthe controlled mode of operation to the master mode of operation basedon a state of the status signal.

In one aspect, the present invention features a method of operating aUPS system having a first UPS and a second UPS coupled in parallel toprovide output power to a load from a power source, each of the firstUPS and the second UPS having an inverter and having a bypass switch,with each UPS configured to operate in one of an inverter mode in whichoutput power is derived from the power source through the inverter, anda bypass mode in which output power is derived from the power sourcebypassing the inverter, the method comprising powering on the first UPSand the second UPS in the inverter mode of operation, designating one ofthe first UPS and the second UPS as a master UPS, and controlling thebypass switch of the first UPS and the bypass switch of the second UPSusing the master UPS.

According to one embodiment, the method further comprises controllingoutput current of the inverter of the first UPS and the output currentof the inverter of the second UPS using the master UPS. In anotherembodiment, the method further comprises detecting that the bypass modeis not available for the first UPS, and in response, preventing thefirst UPS from entering bypass mode. In one embodiment, the methodfurther comprising coupling a connection module between the first UPSand the second UPS.

According to another embodiment, coupling a connection module includescoupling first and second bypass control lines between the first UPS andthe second UPS. In one embodiment, designating one of the first UPS andthe second UPS as a master UPS includes designating the first UPS as themaster UPS, and wherein the method further includes detecting a failurein the first UPS, and in response, designating the second UPS as themaster UPS, and controlling output current of the inverter in the secondUPS using at least one control signal generated by the second UPS. Inanother embodiment, designating one of the first UPS and the second UPSas a master UPS includes designating the first UPS as the master UPS,and wherein the method further includes receiving at the first UPS arequest from the second UPS to operate in bypass mode, controlling thefirst UPS to enter bypass mode, and providing a control signal to thesecond UPS to control the second UPS to enter bypass mode.

In another aspect, the present invention features a UPS comprising afirst input to receive input power from a first power source, a secondinput to receive input power from a second power source, an outputcoupled to provide output power, an inverter coupled to the output andconfigured to provide the output power derived from at least one of thefirst power source and the second power source, a bypass switch coupledto the first input and the second input and configured to bypass theinverter in a bypass mode of operation, a first I/O, a second I/O,control circuitry configured to control the UPS to operate in one of amaster mode of operation and a controlled mode of operation andconfigured in the master mode of operation to control the bypass switchand provide a signal at the first I/O to control a second UPS, andconfigured in the controlled mode of operation to control the bypassswitch based on a control signal received at the second I/O.

According to one embodiment, the control circuitry is further configuredto control output current of the inverter in the master mode ofoperation, and provide an output signal to control output current of thesecond UPS in the master mode of operation. In one embodiment, thecontrol circuitry is configured to detect that a bypass mode is notavailable for the second UPS, and in response, prevent the UPS fromentering the bypass mode of operation. In another embodiment, thecontrol circuitry is configured to receive an input signal from thesecond UPS indicating a failure of the second UPS, and in responsechange a mode of operation of the UPS from the controlled mode ofoperation to the master mode of operation. In another embodiment, thecontrol circuitry is further configured to receive a request from thesecond UPS to operate in bypass mode, and in response, control the UPSto enter bypass mode, and provide a control signal to the second UPS tocontrol the second UPS to enter bypass mode.

In one aspect, the present invention features a UPS system comprising afirst UPS and a second UPS, each of the first UPS and the second UPSincluding a first input to receive input power from a first powersource, a second input to receive input power from a second powersource, an output coupled to provide output power, an inverter coupledto the output and configured to provide the output power derived from atleast one of the first power source and the second power source, abypass switch coupled to the first input and the second input andconfigured to bypass the inverter in a bypass mode of operation, a firstI/O, a second I/O, control circuitry configured to set a mode ofoperation to one of a master mode of operation and a controlled mode ofoperation and configured in the master mode of operation to control thebypass switch and provide a signal at the first I/O to control a secondUPS, and configured in the controlled mode of operation to control thebypass switch based on a control signal received at the second I/O, anda connection module coupled to the first I/O, the second I/O and theoutput of the first UPS and coupled to the first I/O, the second I/O andthe output of the second UPS, the connection module having an outputthat provides output power from at least one of the first UPS and thesecond UPS.

According to one embodiment, the control circuitry of each of the firstUPS and the second UPS is configured in master mode of operation tocontrol output current of the inverter in the first UPS and to controloutput current of the inverter in the second UPS. In one embodiment, thecontrol circuitry in the first UPS is further configured to detect thatthe second UPS is operating in master mode and unable to operate inbypass mode, and in response, prevent the first UPS from entering bypassmode.

According to another embodiment, the connection module is configured toreceive input power and provide the input power to the first UPS and thesecond UPS. In one embodiment, the control circuitry in the second UPSis configured to detect a failure in the first UPS, and in response,designate the second UPS as the master UPS, and control output currentof the inverter in the second UPS. In another embodiment, the controlcircuitry in the first UPS is configured to detect a failure in thesecond UPS, and in response, designate the first UPS as the master UPS,and control output current of the inverter in the first UPS.

According to one embodiment, the control circuitry in the second UPS isfurther configured to detect that the first UPS is operating in mastermode and unable to operated in bypass mode, and in response, prevent thesecond UPS from entering bypass mode. In another embodiment, the controlcircuitry in the first UPS is further configured to receive a requestfrom the second UPS to operate in bypass mode, control the first UPS toenter bypass mode, and provide a control signal to the second UPS tocontrol the second UPS to enter bypass mode.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various FIGS. is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a circuit diagram of a parallel UPS system in accordance withaspects of the present invention;

FIG. 2 is a circuit diagram of a master/controlled detection circuit inaccordance with aspects of the present invention;

FIG. 3 is a schematic diagram of a bypass control logic circuit inaccordance with aspects of the present invention; and

FIG. 4 is a circuit diagram of a UPS in diagnostic mode with paralleldiagnostic connection in accordance with aspects of the presentinvention.

DETAILED DESCRIPTION

Embodiments of the invention are not limited to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. Embodiments of theinvention are capable of being practiced or of being carried out invarious ways. Also, the phraseology and terminology used herein is forthe purpose of description and should not be regarded as limiting. Theuse of “including,” “comprising,” or “having,” “containing”,“involving”, and variations thereof herein, is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems.

As discussed above, to provide enhanced scalability and/or redundancy,two UPS's may be electrically connected to form a single parallel UPSsystem with one output configured to be coupled to a load. In typicalparallel UPS systems, the two UPS's may communicate with each other(e.g., via a bus) to manage their joint operation in the parallel UPSsystem. In such a system, before the parallel UPS system is able tooperate, the two UPS's may need to exchange initial startup informationto define how the two UPS's will interact. These initial startupcommunications may cause delay in the operation of the parallel UPSsystem, and may require complex communication circuitry in each UPS.

At least some embodiments described herein provide a parallel UPS systemin which a first UPS and a second UPS, coupled in parallel, are capableof providing power to a load using a master/controlled approach withoutthe need for complex communications occurring between the two UPS's. Inthis way, the parallel UPS system can provide more immediate power to aload. In addition, as described below, at least some parallel UPSsystems of the present invention also provide additional enhancedfunctionality.

FIG. 1 is a circuit diagram of a parallel UPS system 100 in accordancewith aspects of the present invention. The parallel UPS system 100includes a first UPS 102 and a second UPS 202. Both the first UPS 102and the second UPS 202 are configured to be coupled in parallel via aconnection module 106 (e.g. an SBP (Service Bypass Panel) or PSBP(Parallel Service Bypass Panel)). According to one embodiment, theconnection module 106 includes a first input 101 configured to becoupled to an external power source. The external power source may be asingle or three-phase power source. The connection module 106 alsoincludes a second input 197 configured to be coupled to a bypassexternal power source, however, in other embodiments, the bypass powersource may be a three phase source. In one embodiment, the bypassexternal power source is a single phase power source. In one embodiment,both the first input 101 and the second input 197 may be coupled to thesame single phase or three phase power source.

The connection module 106 is coupled to an output 103 of the first UPS102 and an output 203 of the second UPS 202. An output 108 of theconnection module 106 is coupled to both the first UPS output 103 andthe second UPS output 203. The output 108 is also coupled to an externalload 109. The connection module 106 functions to provide power to eachUPS, receive output power from each UPS, and provide output power to oneor more loads. As discussed below, the connection module 106 alsoprovides additional functionality related to control of each UPS.

The specific components of the first UPS 102 will now be described ingreater detail. The first UPS 102 is substantially the same as thesecond UPS 202 and like components are labeled using similar referencenumbers, except that reference numbers for components of the first UPSstart with the number one and reference numbers for components of thesecond UPS start with the number two.

The first UPS 102 includes a master/controlled detection circuit 110coupled to a current reference select control circuit 120. The currentreference select control circuit 120 is also coupled to a UPS availabledetection circuit 152 and a current reference select switch bank 122.The current reference select switch bank 122 is coupled to a Voltageerror amplifier (Vea) 124 and a Current error amplifier (Cea) 130. TheVea 124 is coupled to a Digital Signal Processor (DSP) 170 via a DCblocking and filter circuit 168 and an inverter 163. The Cea 130 iscoupled to the DSP 170 via a filter and buffer circuit 180 and theinverter 163. The DSP 170 is also coupled to a bypass control circuit160. The Cea 130 is coupled to an inverter controller 182 and theinverter controller 182 is coupled to the inverter 163. The inverter iscoupled to a ±DC bus 199 and to an output 103 of the UPS 102.

The master/controlled detection circuit 110 is configured to receivefour jumper sense signals via four jumper sense Input/Output's (I/O's)(e.g., A sense 112, B sense 114, C sense 116, and D sense 118) coupledto the connection module 106. As described herein, the master/controlleddetection circuit 110 receives four jumper sense signals from fourjumper sense I/O's; however, in other embodiments, the master/controlleddetection circuit may be configured to receive any number of jumpersense signals from any number of jumper sense I/O's. Upon the first UPS102 being coupled to the connection module 106 via a first connector 105and the second UPS 202 being coupled to the connection module 106 via asecond connector 107, the B sense I/O 114 is coupled to the A sense I/O212 and both C sense I/O's 116, 216 are coupled to ground.

The current reference select switch bank 122 includes three switches(e.g., SW1 122 a, SW2 122 b and SW3 122 c), each coupled to the currentreference select control circuit 120. However, in other embodiments, thecurrent select switch bank 122 may include any number of switches. SW1122 a is coupled between the output 126 of the voltage error amplifier(Vea) 124 and a primary bus transmit I/O 128. When SW1 112 a is closed,the output 126 of the Vea 124 is coupled to the primary bus transmit I/O128. The first UPS 102 also includes a primary bus transmit return I/O129 which is coupled to ground 131.

SW2 122 b is coupled between the negative input terminal 132 of thecurrent error amplifier (Cea) 130 and the primary bus transmit I/O 128.When SW2 122 b is closed, the negative input terminal 132 of the Cea 130is coupled to the primary bus transmit I/O 128. SW3 122 c is coupledbetween the output 134 of an amplifier 136 and the negative inputterminal 132 of the Cea 130. When SW3 122 c is closed, the output 134 ofthe amplifier 136 is coupled to the negative input terminal 132 of theCea 130. The negative input terminal 138 of the amplifier 136 is coupledto the output 134 of the amplifier 136 and a primary bus receive I/O142. The positive input terminal 140 of the amplifier 136 is coupled toa primary bus receive return I/O 144 and to ground 146.

Upon the first UPS 102 being coupled to the connection module 106 viathe first connector 105 and the second UPS 202 being coupled to theconnection module 106 via the second connector 107, the primary bustransmit I/O 128 is coupled to the primary bus receive I/O 242, theprimary bus transmit return I/O 129 is coupled to the primary busreceive return I/O 244, the primary bus receive I/O 142 is coupled tothe primary bus transmit I/O 228, and the primary bus receive return I/O144 is coupled to the primary bus transmit return I/O 229.

According to one embodiment, the primary bus transmit I/O 128 isconfigured to provide a PRIM_BUS_TX signal from the output 126 of theVea 124 to the second UPS 202. According to one embodiment, the primarybus receive I/O 142 is configured to receive a PRIM_BUS_RX signal fromthe second UPS 202 and provide the PRIM_BUS_RX signal to the Cea 130.

The UPS available detection circuit 152 is coupled to a UPS availabletransmit I/O 150 and the current reference select control circuit 120.According to one embodiment, the UPS available transmit I/O 150 isconfigured to provide a UPS_AVAIL_TX signal from the UPS availabledetection circuit 152 to the current reference select control circuit120 and the second UPS 202. A UPS available receive I/O 148 is coupledto the current reference select control circuit 120. According to oneembodiment, the UPS available receive I/O 148 is configured to receive aUPS_AVAIL_RX signal from the second UPS 202 and provide the UPS_AVAIL_RXsignal to the current reference select control circuit 120. The UPSavailable detection circuit 152 is also configured to receive UPS faultsignals 154. Upon the first UPS 102 being coupled to the connectionmodule 106 via the first connector 105 and the second UPS 202 beingcoupled to the connection module 106 via the second connector 107, theUPS available receive I/O 148 is coupled to the UPS available transmitI/O 250 and the UPS available transmit I/O 150 is coupled to the UPSavailable receive I/O 248.

The bypass control circuit 160 is coupled to the DSP 170, a bypasscontrol transmit I/O 156 and a bypass control receive I/O 158. Accordingto one embodiment, the bypass control transmit I/O 156 is configured toprovide a BYP_CNTL_TX signal from the bypass control circuit 160 to thesecond UPS 202. According to one embodiment, the bypass control receiveI/O is configured to receive a BYP_CNTL_RX signal from the second UPS202 and provide the BYP_CNTL_RX signal to the bypass control circuit160. Upon the first UPS 102 being coupled to the connection module 106via the first connector 105 and the second UPS 202 being coupled to theconnection module 106 via the second connector 107, the bypass controltransmit I/O 156 is coupled to the bypass control receive I/O 258 andthe bypass control receive I/O 158 is coupled to the bypass controltransmit I/O 256.

The negative input terminal 162 of the Vea 124 is coupled to an invertervoltage sense line 164 from the inverter 163 and to the DSP 170 via theDC blocking and filtering circuit 168. The positive input terminal 172of the Vea 124 is coupled to ground 174. In addition to switches SW2 122b and SW3 122 c, the negative input terminal 162 of the Cea 130 is alsocoupled to an inverter current sense line 176 from the inverter 163 andto the DSP 170 via the filtering and buffer circuit 180.

The output 181 of the Cea 130 is coupled to the inverter controller 182.According to one embodiment, the inverter controller 182 is a hystereticcontroller; however, in other embodiments the inverter controller 182may be any known controller scheme. The controller 182 is coupled to theinverter 163 and the output 184 of the inverter is coupled to the load109 via the output 103 of the first UPS 102 and the output 108 of theconnection module 106.

According to one embodiment, the parallel UPS system 100 includes aController Area Network bus (CAN bus) coupled between the first UPS 102,the second UPS 102 and the connection module 106. For example, a CANhigh bus line 186 and a CAN low bus line 188 may be coupled between thefirst UPS 102 and the second UPS 202 via the connection module 106. BothCAN bus lines 186, 188 may also be coupled to a controller (not shown)within the connection module 106.

The parallel UPS system 100 operates by using a master/controlled UPSapproach where one UPS is designated as the master UPS and the other UPSis designated as the controlled UPS. The master UPS is responsible foroverall control of the power provided to the load 109 and any controlledUPS acts as a current source inverter and shares the load current asdemanded by the master UPS. In one embodiment, either UPS can act as amaster or controlled UPS, and the UPS's can dynamically change theirdesignation as master or controlled if required; however, only one UPSmay be designated as master at any given time.

Upon being connected to the connection module 106, the first UPS 102 andthe second UPS 202 may begin to exchange information via the CAN bus186, 188. Such information may include, but is not limited to:

-   -   Synchronization of UPS settings (output voltage, frequency and        other user settings)    -   Firmware compatibility checkup among units in parallel    -   User view of system data    -   State diagram control of parallel system (to make sure units are        in correct state and proper system operation is ensured).    -   Other less time critical data transfer

In addition to the information exchanged via the CAN bus 186, 188, theUPS's 102, 202 also determine which UPS will operate as master and whichwill operate as controlled. However, because the operation of theparallel UPS system 100 depends on the master/controlled determination,the determination needs to be made relatively quickly. Utilization ofthe CAN bus 186, 188 to make such a determination jointly between UPS'smay result in a delay in providing power to the load 109. As a result,at least some embodiments described herein utilize discrete analog anddigital I/O signals for effective and timely individualmaster/controlled assignments.

Upon coupling the first UPS 102 to the connection module 106 via thefirst connector 105 and coupling the second UPS 202 to the connectionmodule 106 via the second connector 107, each UPS 102, 202 utilizes thejumper sense signals received via the jumper sense Input/Output's(I/O's) (e.g., A sense 112, B sense 114, C sense 116, and D sense 118)to make an individual determination whether it is configured as a masteror controlled UPS and to which connector 105, 107 the UPS is connected.Communications between the UPS's 102, 202 related to themaster/controlled determination are not necessary as each UPS is capableof making an independent evaluation based on the jumper sense signals.

As shown in FIG. 1, each UPS 102, 202 is capable of monitoring fourjumper sense signals via the jumper sense Input/Output's (I/O's) (e.g.,A sense 112, B sense 114, C sense 116, and D sense 118). Theconfiguration of the jumper sense signals determines whether a UPS willoperate as a master or controlled UPS. According to one embodiment, thejumper sense signals are detected by the master/controlled detectioncircuit 110 (e.g., a DSP or Complex Programmable Logic Device (CPLD))upon the UPS's being coupled to the connection module 106 and theparallel UPS system 100 powering up. Based on these sense signals, eachUPS 102 202 will individually determine its own assigned configuration.

FIG. 2 is a circuit diagram of the master/controlled detection circuit110, 210 in accordance with aspects of the present invention. Thespecific components of the master/controlled detection circuit 110 ofthe first UPS 102 will now be described in greater detail. Themaster/controlled detection circuit 110 of the first UPS 102 issubstantially the same as the master/controlled detection circuit 210 ofthe second UPS 202 and like components are labeled using similarreference numbers, except that reference numbers for components of themaster/controlled detection circuit 110 of the first UPS 102 start withthe number one and reference numbers for components of themaster/controlled detection circuit 210 of the second UPS 202 start withthe number two.

The master/controlled detection circuit 110 includes an A sense I/O 112,a B sense I/O 114, a C sense I/O 116 and a D sense I/O 118. The A senseI/O 112 is coupled to the current reference select control circuit 120and to a 12V DC source 123 via a switch 115. The B sense I/O 114 iscoupled to the current reference select control circuit 120 and to a 5VDC source 127. The C sense I/O 116 is coupled to a 5V DC source 135. TheC sense I/O 116 is also coupled to the current reference select controlcircuit 120 and to a 3.3V DC source 147 via a switch 139. The D senseI/O 118 is coupled to the current reference select control circuit 120and to a 5V DC source 151.

For example, according to one embodiment, the A sense I/O 112 is coupledto the base 113 of a transistor 115. The emitter 117 of the transistor115 is coupled to ground 119. The collector 121 of the transistor 115 iscoupled to the 12V DC source 123 and to the current reference selectcontrol circuit 120. The B sense I/O 114 is coupled to the 5V DC source127 and to the current reference select control circuit 12. Also, asdescribed above, upon coupling the first UPS 102 to the connectionmodule 106 and the second UPS 202 to the connection module 106, the Bsense I/O 114 is coupled to the A sense I/O 212.

The C sense I/O 116 is coupled to the 5V DC source 135 and also to thebase 137 of a transistor 139. The emitter 141 of the transistor 139 iscoupled to ground 143. The collector 145 of transistor 139 is coupled tothe 3.3V DC source 147 and to the current reference select controlcircuit 120. Also, upon coupling the first UPS 102 to the connectionmodule 106 and the second UPS 202 to the connection module 106, the Csense I/O 116 is coupled to ground 155 and ground 255, and the C senseI/O 216 is coupled to ground 157 and ground 257. The D sense I/O 118 iscoupled to the 5V DC source 151 and to the current reference selectcontrol circuit 120.

Table 1, shown below, illustrates different operational states or modesof the parallel UPS system 100 in relation to the master/controlleddetermination. As can be seen in FIG. 2 and Table 1, a high C sensesignal 149, 249 indicates to the corresponding current reference selectcontrol circuit 120, 220 that a UPS is correctly coupled to theconnection module 106. For example, if the first UPS 102 is correctlycoupled to the connection module 106, the 3.3V DC source 147 will drivethe C sense signal 149 high. If the first UPS 102 is not correctlycoupled to the connection module 106, the 5V DC source 135 will turn onthe transistor 139 and drive the C sense signal 149 low.

TABLE 1 A - B - C - Sense UPS UPS Master - M/ State Sense Sense SBPPresent D - Sense Mode of Operation AVAIL TX AVAIL RX Controlled - C S1S2 S3 At Power Up Open Open Open 1-Stand 1A 1 1 0 nc Stand Alone nc ncStd Alone Close Close Open Alone Par Cable missing (Main) 1B 1 1 1 ncSBP Conntected nc nc Close Close Open 2-Fault/Diag 2A 0 0 0 0 Par DiagMode nc nc Diag-M Close Open Close 2B 0 0 0 1 Fault nc nc Fault SeeResponse 2C 0 0 1 nc Fault nc nc (M) table below 2D 1 0 0 nc Fault nc nc2E 0 1 0 nc Fault nc nc 3-Parallel 3A 1 0 1 nc UPS1 (Master) 0 (Bad) 0(Bad) M Open Open Open Mode 3B nc 1 (Good) C Open Open Close 3C nc 1(Good) nc M Close Close Open 3D 0 1 1 nc UPS2 (Controlled) 0 (Bad) 0(Bad) M Open Open Open 3E nc 1 (Good) C Open Open Close 3F nc 1 (Good) 0(Bad) M Close Close Open 3G nc 1 (Good) C Open Open Close

As can be seen in FIG. 2 and Table 1, the A sense 125, 225 and B sense133, 233 signals transmitted to the corresponding current referenceselect control circuit 120, 220 control the master/controlled UPSdetermination. When both the A sense signal 125, 225 and B sense signal133, 233 are high, the connected UPS operates as the master UPS in standalone mode. For example, upon coupling only the first UPS 102 to theconnection module 106, the 12V DC source 123 drives the A sense signal125 high and the 5V DC signal 127 drives the B sense signal 133 high,indicating to the current reference select control circuit 120 that thefirst UPS 102 will be operating in stand alone mode (i.e. state 1A or 1Bas seen in Table 1).

Alternatively, upon powering up, the UPS system 100 will be configuredin parallel mode with the first UPS 102 designated as master and thesecond UPS 202 designated as controlled if B sense signal 133 is low, Asense signal 125 is high, C sense signal 149 is high, A sense signal 225is low, B sense signal 233 is high and C sense signal 249 is high. Forexample, upon coupling both the first UPS 102 and the second UPS 202 tothe connection module 206, the 12V DC source 123 drives the A sensesignal 125 high, the 5V DC signal 227 drives the B sense signal 233high, the 3.3V DC source 147 drives the C sense signal 149 high and the3.3V DC source 247 drives the C sense signal 249 high. The 5V DC source127 turns on the transistor 215 consequently driving the B sense signal133 and the A sense signal 225 low. As a result, the current referenceselect control circuit 120 recognizes that that first UPS 102 isdesignated as the master UPS (i.e. state 3A, 3B or 3C as seen inTable 1) and the current reference select control circuit 220 recognizesthat the second UPS 202 is designated as the controlled UPS (i.e. state3D-3G).

As seen in Table 1, other combinations of the A sense 125, 225, B sense133, 233, and C sense 149, 249 signals may result in a fault condition.Also, according to one embodiment, the D sense signals 153, 253 may beutilized to indicate to the corresponding current reference selectcontrol circuit 120, 220 that the UPS system 100 should enter adiagnostic mode. For example, in one embodiment, when D sense 153, 253,A sense 125, 225, B sense 133, 233, and C sense 149, 249 signals are alllow, the UPS system 100 will enter a diagnostic mode. The D sensesignals 153, 253 in relation to the diagnostic mode will be discussed ingreater detail below.

As seen in Table 1, additional signals may also impact the operationalstatus of each of the UPS's coupled in parallel with the UPS system 100.Referring to FIG. 1, in addition to jumper sense signals, each currentreference select control circuit 120, 220 also receives signalsindicating the health of its own UPS and of the other UPS. For example,each UPS generates a UPS_AVAIL_TX signal, indicating if the UPS is ableto supply a load, and provides the signal to the corresponding UPSavailable transmit I/O 150, 250. The UPS_AVAIL_TX signal is generated bya UPS's corresponding UPS available detection circuit 152, 252. The UPSavailable detection circuit 152, 252 monitors a variety of UPS faults154, 254. If any one of the UPS faults indicates a problem with the UPS,the UPS_AVAIL_TX signal will be driven low, indicating that there is aproblem with the UPS. Otherwise, if no problems are detected, theUPS_AVAIL_TX signal is driven high, indicating that there are no healthissues with the UPS.

According to one embodiment, the UPS available detection circuit 152,154 monitors UPS faults such as:

-   -   PRIM_CHK: Fault with error amplifier    -   INTERNAL_FLT_DSP: This signal is generated by the DSP based on        numerous surveillance faults that the DSP monitors and detects.    -   DC_BUS_OV: DC bus voltage faults. In the event of this fault,        the PFC and Inverter need to be disabled immediately and open        the inverter relay.    -   INV_FLT: Inverter hardware fault. The inverter will be disabled        and the inverter relay is opened immediately    -   INV_OV: Inverter over voltage fault. The inverter will be        disabled and the inverter relay is opened immediately    -   IGBT_FAULT: PFC and/or Inverter IGBT fault. In the event of this        fault, the PFC and Inverter need to be disabled immediately and        open the inverter relay.

In other embodiments, other UPS faults may be monitored and any numberof defined combinations may trigger UPS_AVAIL_TX to go low. In addition,each UPS also receives a UPS_AVAIL_RX signal from the other UPS, via theUPS available receive I/O 148, 248, indicating whether the other UPS isable to supply a load. As shown in Table 1, in addition to the jumpersense signals, the health of the UPS's may impact the mode of operationof the parallel UPS system 100.

According to one embodiment and as shown in FIG. 1, both UPS's share acommon current reference signal called PRIM_BUS and each UPS utilizestwo differential control analog signals, PRIM_BUS_TX and PRIM_BUS_RX toprovide or receive the PRIM_BUS signal. The PRIM_BUS_TX and PRIM_BUS_RXdifferential control analog signals are transmitted or received via thecorresponding primary bus transmit and receive I/O's 128, 142, 228, 242within each UPS. The primary bus transmit I/O of one UPS 128, 228 isconnected to the primary bus receive I/O 142, 242 of the other UPS. TheUPS that uses the PRIM_BUS_TX signal for inverter control is consideredthe master UPS, while the UPS that uses PRIM_BUS_RX for inverter controlis considered the controlled UPS. The selection of either PRIM_BUS_TX orPRIM_BUS_RX by a UPS as the appropriate control signal depends on thehealth (i.e. the status of UPS_AVAIL_TX and UPS_AVAIL_RX signals) andstate (i.e. the state of the jumper sense signals) of each UPS.

As described previously, each UPS 102, 202 has its own Vea 124, 224, Cea130, 230, and single pole analog switch bank 122. Each Vea 124, 224receives an inverter voltage sense signal via the inverter voltage senseline 164, 264 from the inverter 163, 263. Each Vea also receives areference voltage signal 166, 266 from the DSP 170, 270 via the DCblocking and filter circuit 168, 268. Each Vea 124, 224 compares theinverter voltage sense signal with the voltage reference signal andgenerates a voltage error signal at the output 126, 226 of the Vea 124,224. The output 126, 226 of the Vea 124 can be coupled to the primarybus transmit I/O 128, 228 through switch SW1 122 a, 222 a and thevoltage error signal can be provided to the primary bus transmit I/O128, 228 as the PRIM_BUS_TX signal. The signal input to the Cea 130, 230(i.e. the current reference signal 189, 289) is taken either from thePRIM_BUS_TX signal via switch SW2 122 b, 222 b or from the PRIM_BUS_RXsignal via the output 134 of the amplifier 136 and switch SW3 122 c, 222c.

In addition to the current reference signal 189, 289, each Cea 130, 230also receives a DC bus balance signal from the DSP 170, 270 via thefilter and buffer circuit 180, 280 and an inverter current sense signalfrom the inverter 163, 263 via an inverter current sense line 176, 276.Based on a comparison of the current reference signal and the invertercurrent sense signal, the Cea 130, 230 provides a current error signalto the inverter controller 182, 282 via the output 181, 281 of the Cea130, 230.

According to one embodiment, AC power supplied by the external powersource to the input 101 is converted to DC power (e.g., via a PowerFactor Correction circuit (not shown)) and supplied to the ±DC bus 199.Based on the current error signal, the inverter controller 182, 282sends control signals to the inverter 163, 263 to convert the DC powerback into regulated AC power. As a result, the inverter 163, 262provides properly regulated AC power to the load 109 from the output184, 284 of the inverter 163, 263.

In another embodiment, where appropriate power from the external powersource is not available at the first input 101, the inverter 163, 263receives DC power from a battery (not shown) coupled to the ±DC bus 199.Based on the current error signal, the inverter controller 182, 282sends control signals to the inverter 163, 263 to convert the DC powerfrom the battery into regulated AC power. As a result, the inverter 163,262 provides properly regulated AC power to the load 109 from the output184, 284 of the inverter 163, 263.

The operation of the switch bank 122, 222 (and hence the operationalmode of each UPS and operation of the parallel UPS system 100) dependson the configuration of each UPS (i.e. the health and jumper status ofeach UPS in the parallel UPS system 100). For example, as seen in Table1 at state 1A and 1B, when the first UPS 102 is defined as the masterUPS (i.e. due to the jumper sense signals signifying that the UPS 102should operate in stand alone mode), switches SW1 122 a and SW2 122 bare closed and switch SW3 122 c is open. In this configuration, thevoltage reference signal at the output 126 of the Vea 124 is provided tothe primary bus transmit I/O 128 as the PRIM_BUS_TX signal via switchSW1 122 a. The PRIM_BUS_TX signal is provided to the Cea 130 as thecurrent reference signal via switch SW2 122 b.

In another example, as seen in Table 1, at states 3A and 3D, when thefirst UPS 102 is defined as the master UPS and the second UPS 202 isdefined as the controlled UPS (i.e. due to the jumper sense signals),the UPS_AVAIL_TX of the first UPS 102 is low (indicating the health ofthe first UPS 102 is bad and consequently that UPS_AVAIL_RX received bythe second UPS 202 from the first UPS 102 is also low), and theUPS_AVAIL_RX signal received by the first UPS 102 from the second UPS202 is low (indicating the health of the second UPS is also bad andconsequently that UPS_AVAIL_TX of the second UPS 202 is also low), allthree switches are opened as both UPS's have failed. Once all threeswitches are opened, the parallel UPS system 100 goes into bypass modeand the inverters 163, 263 are disabled. Bypass mode will be discussedin greater detail below.

In an additional example, as seen in Table 1 at states 3B and 3F, whenthe first UPS 102 is defined as the master UPS and the second UPS 202 isdefined as the controlled UPS (i.e. due to the jumper sense signals),the UPS_AVAIL_TX of the first UPS 102 is low (indicating the health ofthe first UPS 102 is bad and consequently that UPS_AVAIL_RX received bythe second UPS 202 from the first UPS 102 is also low), and theUPS_AVAIL_RX signal received by the first UPS 102 from the second UPS202 is high (indicating the health of the second UPS is good andconsequently that UPS_AVAIL_TX of the second UPS 202 is also high), thefirst UPS 102 is reconfigured as the controlled UPS (because it hasfailed) and the second UPS 202 is reconfigured as the master UPS. As aresult, switches SW1 122 a, SW2 122 b, and SW3 222 c are opened whileswitches SW3 122 c, SW1 222 a, and SW2 222 b are closed. In thisconfiguration, the voltage reference signal at the output 226 of the Vea224 is provided to the primary bus transmit I/O 228 as the PRIM_BUS_TXsignal via switch SW1 222 a. The PRIM_BUS_TX signal is provided to theCea 230 as the current reference signal via switch SW2 222 b. ThePRIM_BUS_TX signal is also provided to the primary bus receive I/O 142as the PRIM_BUS_RX signal. The PRIM_BUS_RX signal is provided, as thecurrent reference signal, to the Cea 130, via the amplifier 136 andswitch SW3 122 c.

In another example, as seen in Table 1 at states 3C, 3E and 3G, when thefirst UPS 102 is defined as the master UPS and the second UPS 202 isdefined as the controlled UPS (i.e. due to the jumper sense signals) andthe UPS_AVAIL_TX of the first UPS 102 is high (indicating the health ofthe first UPS 102 is good and consequently that UPS_AVAIL_RX received bythe second UPS 202 from the first UPS 102 is also high), the first UPS102 maintains its configuration as the master UPS and the second UPS 202maintains its configuration as the controlled UPS, regardless of thehealth status of the second UPS 202. In such a configuration, switchesSW1 122 a, SW2 122 b, and SW3 222 c are closed and switches SW3 122 c,SW1 222 a, and SW2 222 b are open. The voltage reference signal at theoutput 126 of the Vea 124 is provided to the primary bus transmit I/O128 as the PRIM_BUS_TX signal via switch SW1 122 a. The PRIM_BUS_TXsignal is provided to the Cea 130 as the current reference signal viaswitch SW2 122 b. The PRIM_BUS_TX signal is also provided to the primarybus receive I/O 242 as the PRIM_BUS_RX signal. The PRIM_BUS_RX signal isprovided, as the current reference signal, to the Cea 230, via theamplifier 236 and switch SW3 222 c.

As shown in Table 2 below, operational states of the parallel UPS system100 may change during operation. For example, if upon powering up theUPS system 100, a load is not currently coupled to the connection module106, the parallel UPS system will enter a stand-by mode. Once a load iscoupled to the system, the system 100 will enter the appropriate stateaccording to the current configuration of the jumper sense signals.Also, if while in standby mode, a fault occurs, a “Configuration Fault”may be displayed to the user via a user interface (not shown) and theUPS system 100 will be prevented from turning on until the fault iscorrected.

TABLE 2 Description - Par Jumper State Response 1 Valid Cofiguration InStand By mode - respond to Par jumper snese and changes, Latch statewhen output is turned On (latched when In On Mode consider followingState Change: load is turned On) 1A --> 1B: Stay in Original state anddisplay “Config Change Message” and ask for confirmation to change state1B --> 1A: Stay in Original State and display “Config Change” and ask tochk the par cable 1 --> 3: Goto Bypass, display “Config Change” and askfor confirm to resume parallel Op 3 --> 1: Goto Bypass, display “ConfigChange” and ask to chk Par cable and resume parallel Op once the Configis back to Par Mode 2 Illegal State In Stand By mode - display “ConfigFault”, don't allow unit to turn-On but respond to Par jumper snese andchanges In On Mode: X --> 2: Goto Bypass, display “Config Change” andask to chk Par cable and resume a legal state once the Config is back toState 1 or 3 In Par Diag Mode: Recongnized in Stand-by mode only State2A: Diagnostic Self Test to isolate a UPS with Prim_Bus_T/Rx Faults andchk all Par Connector signals - Special Par. Conn will be used.

If while in state 1A (i.e. the UPS is currently uncoupled from theconnection module 106 and in stand alone mode) the UPS is coupled to theconnection module 106, the UPS will remain in state 1A and ask the userfor confirmation that the change to state 1B is desired. If while instate 1B (i.e. the UPS is currently coupled to the connection module 106and in stand alone mode) the UPS becomes disconnected from theconnection module 106, the UPS will notify the user of the connectionproblem and ask the user to check the connection.

If the UPS is in either state 1A or 1B and a switch to paralleloperation is sensed (i.e. any of states 3A-3G), the parallel UPS system100 will enter bypass mode until a user confirms the desire to beginparallel operation. If the parallel UPS system 100 is currentlyoperating in parallel operation and a switch to either state 1A or 1B issensed, the parallel UPS system 100 will enter bypass mode, ask the userto check the UPS connections to the connection module 106, and resumeparallel operation once parallel operation can be resumed.

If the UPS is operating in any on-mode (i.e. stand alone operation orparallel mode operation) and the parallel UPS system 100 enters a faultstate (i.e. state 2B-2E), the parallel UPS system 100 will enter bypassmode, ask the user to check the UPS connections to the connection module106, and resume a legal state once the configuration is back to standalone or parallel operation.

As discussed above, in response to certain operational states of theparallel UPS system 100, the first UPS 102 and the second UPS 202 maydesire to enter a bypass mode. Operation of a bypass mode within theparallel UPS system 100 is controlled by the bypass control circuit 160,260 in each of the UPS's 102, 202. As mentioned previously, as bothUPS's 102, 202 are providing power to the load 109 via the same output108 of the connection module 106, the power provided by both UPS's mustbe carefully managed by the master UPS. Therefore, configuring when aUPS is allowed to enter bypass mode and provide unregulated power to theload 109 must also be carefully managed. As such, according to oneembodiment, the parallel UPS system 100 is capable of operating in avariety of modes.

In a first mode of operation, the bypass control circuit 160, 260 of themaster UPS controls the parallel UPS system 100, so that only one UPS isfeeding the load 109, either from the inverter output 184, 284 or viabypass, at a time. The other UPS does not provide power to the load 109.

In a second mode of operation, the master UPS controls the parallel UPSsystem 100 so that half of the power provided to the load 109 isregulated power generated by the master UPS and half of the powerprovided to the load 109 is regulated power generated by the controlledUPS.

In a third mode of operation, the bypass control circuit 160, 260 of themaster UPS controls the parallel UPS system 100 so that half of thepower provided to the load 109 is unregulated power from the master UPSin bypass mode and half of the power provided to the load 109 isunregulated power from the controlled UPS in bypass mode.

According to one embodiment, the bypass control circuit 160, 260 of themaster UPS determines when a UPS of the parallel UPS system 100 entersbypass mode by following two redundancy objectives. The first redundancyobjective is that upon component failure (i.e. UPS_AVAIL_TX/RXindicating a failed UPS); each UPS should change their mode so thattheir combined power output to the load 109 is maintained. The secondredundancy objective is that each UPS should select their bypass mode insuch a way that their combined state minimizes component stress (e.g.,battery, power electronics, etc.) to extend the life of the system 100.

Also, according to one embodiment, the bypass control circuit 160, 260prevents the parallel UPS system 100 from providing a portion ofregulated power from one UPS and a portion of unregulated power from theother UPS to the load 109. To avoid such a situation, bypass switches ofparalleled UPS's are controlled in unison by the single master UPS.

In one embodiment, a user can request the bypass operation from thecontrolled UPS's interface. The controlled UPS, in turn, sends a requestto the master UPS, requesting entry into bypass mode. This bypasscontrol handshake is done by exchanging the digital signal BYP_CNTL_TXas depicted in FIG. 3.

FIG. 3 is a schematic diagram of a bypass control logic circuit 160, 260in accordance with aspects of the present invention. As seen in FIG. 1,each bypass control logic circuit 160, 260 is coupled to the DSP 170,270. Each bypass control logic circuit 160, 260 is also coupled to thebypass control transmit I/O 156, 256, to the bypass control receive I/O158, 258, and to a bypass switch control line 193, 293. Each bypassswitch control line 193, 293 is coupled to a bypass switch 195, 295 andeach bypass switch 195, 295 is coupled between the load 109 and theexternal bypass power source coupled to the second input 197. Uponcoupling the first UPS 102 and the second UPS 202 to the connectionmodule, the bypass control transmit I/O 156 is coupled to the bypasscontrol receive I/O 258 via the connection module 106 (not shown) andthe bypass control receive I/O 158 is coupled to the bypass controlreceive I/O 256 via the connection module 106 (not shown).

If the parallel UPS system 100 is to enter bypass mode, the bypasscontrol logic circuit 160, 260 sends bypass switch control signals tothe bypass switch 195, 295 via the bypass switch control line 193, 293to operate the bypass switch 195, 295 to couple the load 109 directly tothe external bypass power source coupled to the second input 197,providing unregulated power directly to the load 109.

As seen in FIG. 1, each UPS's bypass control circuit 160, 260 receivesreference information 191, 291 from the DSP 170, 270. According to oneembodiment, the reference information 191, 292 includes informationregarding the condition of the corresponding UPS. For example, suchcondition information may include information regarding synchronizationwith a corresponding inverter, bypass voltage health, UPS health, a userinterface communication/request, information regarding a current stateor state change request, or any other information related to whether thecorresponding UPS should enter bypass mode. Based on the receivedconditions, the bypass control circuit 160, 260 determines whether a UPSshould enter bypass mode.

According to one embodiment, if the bypass control circuit 160 of amaster UPS 102 determines that the UPS 102 should enter bypass mode(e.g., in response to a user request or a condition that requires theUPS to go to bypass), the bypass control circuit 160 confirms thatbypass is available, informs the bypass control circuit 260 of thecontrolled UPS 202 that the master UPS 102 is going into bypass (via ahigh BYP_CNTL_TX signal on the bypass control transmit I/O 156 andconsequently a high BYP_CNTL_RX signal on the bypass control receive I/O258), and activates the bypass switch 195 of the UPS 102 to enter bypassmode and provide unregulated power to the load 109.

If, upon entering bypass mode, the bypass control circuit 160 of themaster UPS 102 determines that the UPS's inverter 163 is available toprovide appropriate regulated power, the bypass control circuit 160 ofthe master UPS 102 will control the master UPS 102 to exit bypass modeand inform the bypass control circuit 260 of the controlled UPS 102 thatthe master UPS 102 is no longer in bypass mode (via a low BYP_CNTL_TXsignal on the bypass control transmit I/O 156 and consequently a lowBYP_CNTL_RX signal on the bypass control receive I/O 258).

If the bypass control circuit 160 of the master UPS 102 receives abypass request from the controlled UPS 202 (i.e. in the form of a highBYP_CNTL_TX signal on the bypass control transmit I/O 256 andconsequently a high BYP_CNTL_RX signal on the bypass control receive I/O158), as long as bypass is available at the time of the request, thebypass control circuit 160 will put the master UPS 102 into bypass mode.However, if at the time of the bypass request by the controlled UPS 202,bypass is not available in the master UPS 102, the master UPS 102 andthe controlled UPS 202 will switch master/controlled designations andthe new controlled UPS 102 will cede control of the two parallel UPS'sto the new master UPS 202.

According to another embodiment, if a bypass control circuit 260 of acontrolled UPS desires to enter bypass mode (e.g., in response to a usercommand or condition that requires the UPS to do so); as long as bypassis available to the controlled UPS 202, the bypass control circuit 260will send a bypass request to the master UPS 102 (i.e., in the form of ahigh BYP_CNTL_TX signal on the bypass control transmit I/O 256 andconsequently a high BYP_CNTL_RX signal on the bypass control receive I/O158). As discussed above, upon receiving a request from the controlledUPS 202, as long as bypass is available, the bypass control circuit 160of the master UPS 102 will drive the master UPS 102 into bypass mode.

Upon seeing the master UPS 102 enter bypass mode (i.e. the highBYP_CNTL_TX signal on the bypass control transmit I/O 156 andconsequently a high BYP_CNTL_RX signal on the bypass control receive I/O258), the bypass control circuit 260 will immediately drive thecontrolled UPS 202 into bypass mode to follow the master UPS 102.

In one embodiment, if bypass in the controlled UPS 202 is not available,but the bypass control circuit 260 sees that the master controller 160has entered bypass mode (i.e. the high BYP_CNTL_TX signal on the bypasscontrol transmit I/O 156 and consequently a high BYP_CNTL_RX signal onthe bypass control receive I/O 258), the controlled UPS 202 willdeactivate as the controlled UPS 202 cannot provide regulated power tothe load 109 while the master UPS 102 is providing unregulated power.According to one embodiment, if bypass is not available on at least oneof the UPS's, the parallel UPS system 100 may ignore bypass requests.

As mentioned above, the parallel UPS system 100 may enter a diagnosticmode if all of the jumper senses (A-D) are low. According to oneembodiment, the diagnostic mode can only be entered from standby modeand the diagnostic mode is a self test mode used to isolate a UPS withPRIM_BUS_TX/RX faults and to check all connection module signals.

As described above in relation to Table 1, upon detection of a fault inany one of the paralleled UPS's, the faulty UPS will be selectivelyisolated while power is still provided from the power output of theparallel UPS system 100. In some cases, system faults may be detected ina parallel UPS system, with the faults occurring in a manner such thatit is difficult to isolate the faults to one UPS. For example, whenfaults occur with circuit portions of a UPS that are shared or connectedto other paralleled UPS's via signal wires, it may be difficult toisolate the faults in either parallel or stand-alone modes. When such afault occurs in the field, it may be necessary in prior systems to sendboth UPS's in a system in for repair, when only one of the UPS's is infact faulty. For example, in reference to the parallel UPS system 100 ofFIG. 1, if a fault exists somewhere within one of the primary bustransmit I/O's 128, 228 or within one of the primary bus receive I/O's142, 242, because the transmit and receive I/O's are coupled togetherdirectly via the connection module 106, it may not be possible for theparallel UPS system 100 to determine which UPS is the source of thefault.

At least some embodiments described herein provide a system and methodfor identifying a faulty UPS in a system wherein the faults occur withinshared circuit portions between paralleled UPS's.

FIG. 4 is a circuit diagram of the first UPS 102 (as described inrelation to FIGS. 1, 2 and 3) configured in a diagnostic mode withparallel diagnostic connector 400 in accordance with aspects of thepresent invention. When a user of a parallel UPS system 100 wishes toindividually test the operation of a single UPS (e.g., the first UPS102), the first UPS 102 is disconnected from other UPS's and key controland status signals are wrapped around back towards the first UPS 102 asshown in FIG. 4 by a test connector 400 (e.g., a parallel diagnosticconnection). According to one embodiment, the first UPS 102 may bedisconnected manually from the connection module 106 (and as a resultfrom a second UPS 202) and instead, manually connected to the testconnector 400 by a user. According to one embodiment, if a user wishesto test both UPS's individually, the second UPS 202 is also disconnectedmanually from the connection module 106 and instead, manually connectedto a second test connector by the user.

According to another embodiment, the test connector 400 is locatedwithin the connection module 106, and the connection module 106 includesrelays that are configured, upon activation of the self diagnostic modein the first UPS 102, to automatically disconnect the first UPS 102 fromthe connection module 106 (and consequently the second UPS 202) andinstead couple the first UPS 102 to the test connector 400 to wrap thekey control and status signals around back towards the first UPS 102 asshown in FIG. 4. According to one embodiment, upon completion ofoperational testing of the first UPS 102 and upon activation of the selfdiagnostic mode in the second UPS 202, the relays of the connectionmodule 106 disconnect the first UPS 102 from the connection module 106and instead couple the second UPS 202 to the test connector 400 to wrapthe key control and status signals back towards the second UPS 202similarly as shown in FIG. 4.

According to one embodiment, when the first UPS 102 is in standby mode,if the first UPS 102 is disconnected from the connection module 106 andis instead coupled to the test connector 400, the D sense I/O 118 iscoupled to ground 155 and ground 157, driving the D sense signal 153low. In addition, upon the first UPS 102 being coupled to the testconnector 400, the A sense I/O 112 is coupled to the B sense I/O,causing the 5V DC source 127 to turn on the transistor 115, resulting inthe A sense signal 125 and B signal 133 being driven low. Also, becausethe first UPS 102 is not connected to the connection module 106, the Csense signal 149 is also driven low.

In addition, once the first UPS 102 is coupled to the test connector400, the primary bus receive I/O 142 is coupled to the primary bustransmit I/O 128, the primary bus receive return I/O 144 is coupled tothe primary bus transmit return I/O 129, the bypass control transmit I/O156 is coupled to the bypass control receive I/O 158, and the UPSavailable receive I/O 148 is coupled to the UPS available transmit I/O.In this way, signals provided to any of the I/O's by the first UPS 102will also be received by I/O's of the first UPS 102.

As shown in Table 1, all four of the sense signals (A, B, C and D) beinglow indicates to the current reference select control circuit 120 thatthe first UPS 102 is in a self diagnostic mode. Also as seen in Table 1,in response to the self diagnostic mode of first UPS 102, switches SW1122 a and SW3 122 c are closed and switch SW2 122 b is open. In thisconfiguration, the voltage reference signal at the output 126 of the Vea124 is provided to the primary bus transmit I/O 128 as the PRIM_BUS_TXsignal via switch SW1 122 a. The PRIM_BUS_TX signal is also received bythe primary bus receive I/O 142 as the PRIM_BUS_RX signal and providedto the Cea 130 as the current reference signal via switch SW3 122 c.

After the first UPS 102 recognizes that it is in self diagnostic mode,it performs an inverter self test to make sure that all of thecomponents of the UPS 102 are working appropriately. If there is afault, (e.g., an issue with a common parallel circuit portion such asprimary bus transmit I/O 128 or primary bus receive I/O 142), then thefirst UPS is identified as having a fault. According to one embodiment,while in self diagnostic mode, the operational status of the bypasscontrol I/O's (bypass control transmit I/O 156 and bypass controlreceive I/O 158) and the UPS available I/O's (UPS available transmit I/O150 and UPS available receive I/O 148) is also confirmed. Also, inanother embodiment, the bypass switch 195 (seen in FIG. 3) will beprohibited from turning on as long as the test connector 400 is coupledto the UPS 102.

Even though examples in accordance with the present invention aredescribed herein with reference to the use of one or two UPS's 102, 202in a parallel UPS system 100, other examples may utilize more than twoUPS's coupled together in parallel

Even though examples in accordance with the present invention aredescribed herein in reference to Uninterruptible Power Supplies (UPS),other examples may be utilized with any type of parallel power system inwhich dual power sources are desired to be coupled together andcontrolled effectively and efficiently. It also is to be appreciatedthat examples in accordance with the present invention may be utilizedto monitor any type (e.g., commercial or residential) or size system.

By providing a parallel UPS system in which a first UPS and second UPS,coupled in parallel, are capable of providing power to a load using amaster/controlled approach and independently determining theirappropriate master/controlled determination, absent the exchange ofinitial master/controlled configuration information between the UPS's,the parallel UPS system is able to more efficiently provide power to aload without unwanted delay. In addition, based on master/controlledjumper signals, UPS availability signals and bypass control signals, theparallel UPS system is capable of providing additional functionality asdescribed above.

Also, by providing a system and method for the determination of faultyUPS's based on faults identified within shared circuit portions betweenparalleled UPS's, a parallel UPS system is able to isolate a UPS havinga fault in a circuit portion in common or shared with other paralleledUPS's.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. Accordingly, the foregoing description and drawings areby way of example only.

What is claimed is:
 1. A method of operating an Uninterruptible PowerSupply (UPS) system having a first Uninterruptible Power Supply (UPS)and a second UPS, the method comprising: coupling at least one controlline between the first UPS and the second UPS to operate the first UPSand the second UPS in a parallel mode of operation; providing outputpower from each of the first UPS and the second UPS to a load; detectinga fault condition in the UPS system; decoupling the at least one controlline in response to detecting the fault condition; operating the firstUPS in a diagnostic mode of operation in response to decoupling the atleast one control line; and determining if the fault condition isassociated with the first UPS, wherein coupling at least one controlline between the first UPS and the second UPS includes coupling aconnection module between the first UPS and the second UPS, and whereindecoupling the at least one control line includes disconnecting theconnection module from the first UPS.
 2. The method of claim 1, furthercomprising: operating the second UPS in a diagnostic mode of operationin response to decoupling the at least one control line; and determiningif the fault condition is associated with the second UPS.
 3. The methodof claim 2, wherein disconnecting the connection module from the firstUPS includes manually disconnecting the connection module from the firstUPS and coupling a diagnostic connector to the first UPS.
 4. The methodof claim 3, wherein determining if the fault condition is associatedwith the second UPS includes coupling a diagnostic connector to thesecond UPS.
 5. The method of claim 2, wherein disconnecting theconnection module from the first UPS includes changing a state of theconnection module from an operational state to a diagnostic state. 6.The method of claim 1, wherein operating the first UPS in the diagnosticmode of operation includes disabling a bypass mode of operation of thefirst UPS.
 7. The method of claim 1, wherein operating the first UPS inthe diagnostic mode of operation includes conducting a self-test of aninverter of the first UPS.
 8. An Uninterruptible Power Supply (UPS)system comprising: a first Uninterruptible Power Supply (UPS) and asecond UPS, each of the first UPS and the second UPS including: a firstinput to receive input power from a first power source; a batteryconfigured to provide battery power; an output coupled to provide outputpower; output power circuitry coupled to the output and configured toprovide the output power derived from at least one of the first powersource and the battery; a first I/O; a second I/O; and control circuitrycoupled to the first I/O and the second I/O; and a connection modulecoupled to the first I/O, the second I/O and the output of the first UPSand coupled to the first I/O, the second I/O and the output of thesecond UPS, the connection module having an output that provides outputpower from at least one of the first UPS and the second UPS; wherein thefirst UPS is configured to operate in a diagnostic mode based on asignal detected at the second I/O of the first UPS, and configured inthe diagnostic mode to determine if a fault of the UPS system isassociated with the first UPS.
 9. The UPS system of claim 8, wherein theconnection module is configured to operate in a diagnostic mode tocouple the first I/O of the first UPS to the second I/O of the firstUPS.
 10. The UPS system of claim 8, further comprising a diagnosticconnector configured to be coupled to the first UPS in the diagnosticmode and configured to couple the first I/O of the first UPS to thesecond I/O of the first UPS.
 11. The UPS system of claim 8, wherein thefirst UPS includes an inverter, and wherein the first UPS is configuredto conduct an inverter test in the diagnostic mode.
 12. The UPS systemof claim 11, wherein the first UPS is further configured to operate in abypass mode of operation, and wherein the control circuitry isconfigured to disable the bypass mode of operation in the diagnosticmode.
 13. The UPS system of claim 8, wherein the second UPS isconfigured to operate in a diagnostic mode based on a signal detected atthe second I/O of the second UPS, and configured in the diagnostic mode,to determine if a fault of the UPS system is associated with the secondUPS.
 14. The UPS system of claim 13, wherein the connection module isconfigured to operate in a diagnostic mode to couple the first I/O ofthe second UPS to the second I/O of the second UPS.
 15. The UPS systemof claim 14, further comprising a diagnostic connector configured to becoupled to the second UPS in the diagnostic mode and configured tocouple the first I/O of the second UPS to the second I/O of the secondUPS.
 16. An Uninterruptible Power Supply (UPS) system comprising: afirst Uninterruptible Power Supply (UPS) and a second UPS, each of thefirst UPS and the second UPS including: a first input to receive inputpower from a first power source; a battery configured to provide batterypower; an output coupled to provide output power; output power circuitrycoupled to the output and configured to provide the output power derivedfrom at least one of the first power source and the battery; a firstI/O; a second I/O; and control circuitry coupled to the first I/O andthe second I/O; and a connection module coupled to the first I/O, thesecond I/O and the output of the first UPS and coupled to the first I/O,the second I/O and the output of the second UPS, the connection modulehaving an output that provides output power from at least one of thefirst UPS and the second UPS; and means, configured to be coupled to atleast one of the first UPS and the second UPS, for detecting a fault inthe UPS system and for isolating the fault to one of the first UPS andthe second UPS.
 17. The UPS system of claim 16, wherein the means fordetecting a fault include means for disabling the output of the firstUPS and the output of the second UPS after detection of a fault.
 18. TheUPS system of claim 16, wherein each of the first UPS and the second UPSincludes parallel control circuitry for operating the first UPS and thesecond UPS in a parallel mode of operation, and wherein the means fordetecting a fault includes means for detecting a fault in the parallelcontrol circuitry of one of the first UPS and the second UPS.
 19. TheUPS system of claim 18, further comprising means for establishing one ofthe first UPS and the second UPS as a master UPS of the UPS system. 20.The UPS system of claim 19, wherein the master UPS is configured tocontrol an output of an inverter in the first UPS and an output of aninverter in the second UPS.